Corrosion inhibiting composition for coating metal, coated metal and method of coating



CORROSION :1 ITING COR POSITION FOR COATING METAL, COATED h IETAL ANDWTHOD F COATING No Drawing. Application May 7, 1954, Serial No. 428,381

14 Claims. c1. 148--6.2)

This invention relates to inhibiting the corrosion of articles andobjects having surfaces of metal which is normally corroded by theaction of the moist atmosphere and in particular by contact with seawater or sea Water spray.

The metals so corroded include in particular iron and steel, aluminum,magnesium, and copper, bi-metallic systems such as aluminum-magnesium orsteel-aluminum, and alloys of these metals which are subject tocorrosion as above indicated. Surfaces of other normally corr-odiblemetals may also be treated eifectively, to inhibit corrosion, inaccordance with this invention.

The subject of corrosion inhibition has been studied extensively overmany years, in an effort to minimize the very considerable economiclosses which occur, during both use and storage, as a result :of suchcorrosion of metallic surfaces, especially those of ferrous metals, butmore recently also those of aluminum and magnesium. Various solutions tothe problem have been advanced along many lines, including the platingof readily corrodible metals with metals which are morecorrosionresistant, the use of corrosion-resistant alloys, and the useof protective wrappings, coverings, and coatings or films. The presentinvention concerns corrosion inhibitors which fall Within the broadclass of protective coatings or films.

Paints of more or less conventional drying-oil-base types, and alsogreases and oils, have been used for many years as protective coatingsfor the surfaces of corrodible metals. Protective films, such as thoseformed by phosphatizing or Bonderizing, have also been used for a numberof years for such purposes. Such films are comrnonly made by treatingthe surface in an aqueous weakly acid solution containing thephosphating or other inhibiting chemicals. This latter procedure, whichis timeconsuming and involves a number of other difiiculties inapplication, produces an adherent film or layer which is in the natureof a reaction product of the inhibitor and the metal of the surface.Although these coatings and films are satisfactory for a number ofpurposes, each one has one or more of a number of limitations. Many ofthem do not offer effective protection against the severe corrosiveeifects of sea or saline waters and spray; greases and oils collect dirtand grit and present difficult handling problems; conventional paintscannot be advantageously removed when it is desired to expose theoriginal surface (for example the interior of the cylinders of internalcombustion engines which are to be kept in storage and protected againstcorrosion); conventional films produced by aqueous methods requireextended treatment in order to be effective.

The inhibitors of the present invention are distinctly superior, ineffectiveness and in convenience of application, to anycorrosion-inhibiting compounds or compositions of which I am aware. Asthese inhibitors are oilsoluble, they can be incorporated with suitabletypes of paints, with oils or greases, or with various kinds ofstrippable-film coating materials. The resulting coatings 2,816,051Patented Dec. 10, 1957 may therefore be of a permanent nature (paints),or may be removable by wiping ofi (oils or greases) or by stripping. Theinhibitors of this invention may be incorporated in priming coatings,which are applied to the metal surface to be protected and then coveredby a paint, which may be a conventional paint or which may include acorrosion inhibitor. Alternatively, these inhibitors may be incorporatedin a volatile solvent and applied to the metal surface to be protected,to form a film or layer which appears to be a reaction product of theinhibitor and the metal. This film may, if desired, be furtherprotected, as by the above described paints, oils, greases, orstrippable film containing inhibitors of this invention, or byconventional paints, oils, greases or strippable films. Furthermore,some of the inhibitors of this invention are capable of beingvolatilized and thus can be used as vapor-phase inhibitors by exposingthe surfaces to be protected to the vapors.

The corrosion inhibitors of this invention are organic esters of certainacidic oxides of metals, in particular of chromic acid H CrOorthovanadic acid H VO metavanadic acid H V O and molybdic acid H MoOThese esters are representable by the formulas R CrO R V0 R V O and RMoO -In the case of the chromates, R represents the radical of atertiary alcohol ROI-I, while in the cases of the orthovanadates, themetavandates and the molybdates, R represents the radical of anyalcohol, whether primary, secondary or tertiary. Each R, and also eachR, in any given compound, may be the same or dilferent, and may bealkyl, aryl, aryl-alkyl, or 'heterocyclic, and is preferably althoughnot necessarily a hydrocarbon radical. It will be noted that the primaryand secondary esters of chromic acid are not included, due to the factthat these are oxidized to ketones and aldehydes in the presence ofchromic acid.

Esters of acidic oxides of other metals, such as RMnO and R WO.,,, whereR and R are as defined above, may also be used as corrosion inhibitorsin accordance with the present invention.

' The most effective of the corrosion inhibitors of this invention arethe esters of 'chromic acid with tertiary alcohols, as represented bythe formula R CrO given above. Typical of these compounds are thedi-esters of chromic acid-with any of the following tertiary alcohols:cedrol, l-methyl borneol, methyl fenchol, alpha terpineol and otherterpineols, triphenyl c-arbinol, tri *(rnethylcyclohexyl) carbinol,dip'henyl methyl carbinol, diphenyl pentadecyl carbinol, S-ethylS-pentadecanol, fi methyl S-tetradecanol, S-butyl 5-nonanol,4,7-dimethyl 4,7-decandiol, octadecyl l-cyclohexanol, tertiary butanol,and Z-methyl 2-butan-ol.

Examples of esters of acidic oxides of other metals hereinabo-vereferred to include tribenzyl vanadate, tricyclohexyl vanadate,tricedryl vanadate, the lower alkyl orthoand meta-vanadates (trimethyl,tripropyl, etc., vanadate), dimethyl moly-bdate, dipentadecyl molybdate,diamyl tungstate, and ditertiary 'butyl permanganate.

-It should be noted that the ease of hydrolyzing increases as themolecular weight of the alcohol component of the ester decreases. Thispermits considerable latitude in selecting esters which will offer thedesired ease of, or resistance to, hydrolysis.

For use, the corrosion inhibitors of this invention are incorporated, asalready indicated, in appropriate coating or carrying media so that theymay be applied, by brushing, spreading, spraying, dipping, or the like,to the surfaces to be protected. The coating or carrying media arepreferably non-aqueous, although Water may be present if more or lesshydrolysis of the esters is desired.

The coating or carrying medium must of course be one which is notdecomposed or otherwise adversely affected by the corrosion inhibitor.Drying oils are as a rule un- Q satisfactory, since they set up soquickly in the presence of the corrosion inhibitor as to make theirapplication to surfaces impractical or impossible. In fact, many of thecorrosion inhibitors herein referred to are used, or usable, as paintdriers. Non-dryingoils-laud the like, such as the fatty glycerides andvarious petroleum oils and greases, are suitable.

Coating media which form solid protective layers, either of the painttype or the strippable-film type, are generally preferred, as they canbe most readily and cleanly applied and become set to provide aneffective sealing layer over the surface to be protected. These mediainclude various synthetic resins, notably the vinyl resins, as well asnatural resins such as shellac.

The corrosion inhibitor is most effective when present in solution inthe coating or carrying composition, but may also be effective whenpresent as a dispersion. While some of the coating media referred toabove are solvents for some of the corrosion inhibitors of thisinvention, it is usually desirable to employ another substance which isa solvent for both. This solvent is volatilized as the coating sets. Onthe other hand, when the film-forming procedure is followed, theinhibitor may 'be dissolved in a solvent as a carrier, the resultingsolution applied to the metal surface to be protected, and the solventvolatilized, as already pointed out.

The amount of corrosion inhibitor in such a coating composition orcarrying solution, or other vehicle, may be varied over a wide range.Preferably, however, the amount of inhibitor should not be in excess ofthe maximum amount thereof which is soluble in the coating composition,carrying solution, or other vehicle during manufacture and in use.

A very effective corrosion-inhibiting coating composition, in accordancewith this invention, may be prepared by mixing together cedryl chromateand a vinyl chloridevinyl acetate (87%-l3%) cop-oly-mer resin, each ofwhich is in solution in a mutual solvent, of which various ones in theclass of ketones and esters are known for the purpose. The proportionsof chromate and resin are such as to provide 3.5 parts by weight CrO to90 parts by weight of the resin. The resulting product, afterapplication to and setting upon a bimetallic magnesiumaluminum surface,protected the surface effectively against corrosion for over 1900 hoursin the presence of salt spray, a very severe test, whereas conventionalzinc chromate primer inhibitor failed in protective effect in less than340 hours.

Another efiective corrosion-inhibiting composition may be prepared bymixing cedryl chromate with lubricating oil, of viscosity SAE 50 forexample, and in an amount such that the cedryl chromate is somewhat inexcess of the amount that will dissolve in the oil. The resulting oilycomposition, when brushed onto an iron surface (e. g. an engine block ora cylinder surface) turns a brownish color, as though rust were present,but examination shows that rust is absent and that the surfaces thuscoated are very effectively protected against corrosion. Thiscomposition may be removed, for example, by a solvent, leaving aninvisible, highly corrosion-resistant film.

As another example of corrosion inhibition in accordance with thisinvention, a solution of tertiary butyl chromate in tertiary butylalcohol is prepared, and is applied to a clean magnesium surface bybrushing, spraying or dipping, after which the surface is drained, anddried at room temperature. A brownish film (rather than a coating, as inthe two preceding examples) is thus formed upon the surface, whichlatter is thereupon highly resistant to corrosion. in contrast, the bestof the known chromate film treatments for magnesium require applicationby a hot aqueous solution which must be maintained in contact with themagnesium surface for at least 20 minutes, i

I claim:

1. The combination of a metal surface normally corrodible by contactwith moist atmospheres and with sea water, and a coating compositioncovering said surface, said coating composition consisting essentiallyof an effective corrosion-inhibiting amount of an ester selected fromthe group consisting of R CrO R VO R' V O R MoO and R' WO wherein R andR are hydrocarbon radicals of the alcohols ROH and ROH respectively andare members of the group consisting of alkyl, aryl, aryl-alkyl andheterocyclic, and R is a tertiary radical, together with a carrier forsaid ester.

2. The combination of a metal surface normally corrodible by contactwith moist atmospheres and with sea water, and a coating compositioncovering said surface,

said coating composition consisting essentially of an effectivecorrosion-inhibiting amount of cedryl chromate and a carrier therefor.

3. The combination of a metal surface normally corrodible by contactwith moist atmospheres and with sea water, and a film on said surfaceconsisting essentially of a reaction product of said surface with anester selected from the group consisting of R CrO R' VO R V O R MoO andR' WO wherein R and R are hydrocarbon radicals of the alcohols ROH andROH respectively and are members of the group consisting of alkyl, aryl,aryl-alkyl and heterocyclic, and R is a tertiary radical.

4. The combination in accordance with claim 3, Wherein said ester istertiary butyl chromate.

5. The combination in accordance with claim 3, wherein said metalsurface is magnesium and said ester is tertiary butyl chromate.

6. A corrosion inhibiting composition consisting essentially of cedrylchromate, a vinyl resin, and a mutual solvent.

7. A corrosion inhibiting compositionconsisting essentially of cedrylchromate and 1a petroleum oil.

8. The method of inhibiting corrosion of a metal surface normallycorrodi'ble by contact with moist atmospheres and with sea water, whichcomprises applying to said surface a composition consisting essentially,of a corrosion-inhibiting amount of an ester selected from the groupconsisting of R CrO R VO R V O R MoO and R WO4, wherein R and R arehydrocarbon radicals of the alcohols ROH and ROH respectively and aremembers of the group consisting of alkyl, aryl, .aryl-alkyl andheterocyclic, and R is atertiary radical, together with a carrier forsaid ester.

9. The method of-inhibiting corrosion of .a metal surface normallycorrodible by contact with moist atmospheres and with sea water, whichcomprises applying to said surface an ester selected from the groupconsisting of R2CI'O4, R3VO4, R V O R'2MOO4, and R'2WO4, Wherein R and Rare hydrocarbon radicals of the alcohols ROH and ROH respectively andare members of the group consisting of alkyl, aryl, aryl-alkyl andheterocyclic, and R is a tertiary radical, a medium which is inert tosaid ester and which is capable of forming a coating layer, and a mutualsolvent for said ester and said medium, and then removing said solvent.

-10. The method of inhibiting corrosion of a metalsurface normallycorrodible by contact with 'moist atmospheres and with sea water, whichcomprises applying to said surface a composition consisting essentiallyof cedryl chromate, a vinyl resin, and a mutual solvent for said esterand for said resin, and then volatilizing said solvent.

11. The method of inhibiting corrosion of a metal surface normallycorrodible by contact with moist atmosphe-res and with sea water, whichcomprises applying to said surface a solution of tertiary butyl chromatein :tertiary butyl alcohol, and then volatilizing said alcohol byexposure to normal room temperature.

12. The method of inhibiting corrosion of magnesium,

which comprises providing a clean surface on said magnesium, applyingsaid surface a solution of about 30 percent tertiary butyl chromate intertiary butyl alcohol, and then removing said alcohol by volatilizationat normal room temperature.

13. The method of inhibiting corrosion of a metal surface normallycorrodible by contact with moist atmospheres and with sea water, whichcomprises volatilizing adjacent to said surface an ester selected fromthe group consisting of R CrO R VO R' V O R MoO and R' WO wherein R andR are hydrocarbon radicals of the alcohols ROH and R'OH respectively andare members of the group consisting of alkyl, aryl, aryl-alkyl andheterocyclic, and R is a tertiary radical, together with a carrier forsaid ester.

14. The method of inhibiting corrosion of a metal surface normallycorrodible by contact with moist atmospheres and with sea water, whichcomprises applying to said surface a solution consisting essentially ofan ester selected from the group consisting of R CrO R VO R' V O R' MoOand R WO wherein R and R are hydrocarbon radicals of the alcohols ROHand R'OH respectively and are members of the group consisting of alkyl,aryl, aryl-alkyl and heterocyclic, and R is a tertiary radical, and asolvent for said ester, and then removing said solvent.

References Cited in the file of this patent UNITED STATES PATENTS

8. THE METHOD OF INHIBITING CORROSION OF A METAL SURFACE NORMALLYCORRODIBLE BY CONTACT WITH MOIST ATMOSPHERES AND WITH SEA WATER, WHICHCOMPRISES APPLYING TO SAID SURFACE A COMPOSITON CONSISTING ESSENTIALLYOF A CORROSION-INHABITING AMOUNT OF AN ESTER SELECTED FROM THE GROUPCONSISTING OF R2CRO4, R''3VO4, R''3V3O9, R''2MOO4, AND R''2WO4, WHEREINR AND R'' ARE HYDROCARBON RADICALS OF THE ALCOHOLS ROH AND R''OHRESPECTIVELY AND ARE MEMBERS OF THE GROUP CONSISTING OF ALKYL, ARYL,ARYL-ALKYL AND HETEROCYCLIC, AND R IS A TERTIARY RADICAL, TOGETHER WITHA CARRIER FOR SAID ESTER.